Managing Dieback 

Phosphite

Phosphite (phosphonate), is a biodegradable fungicide that protects plants against Phytophthora dieback. Phosphite works by boosting the plant's own natural defences and thereby allowing susceptible plants to survive within Phytophthora dieback infested bushland.

It is important to note that there is no chemical that will eradicate Phytophthora dieback, including phosphite. However, an integrated approach can successfully control the spread and impact of the disease. An integrated approach may combine strategic phosphite treatment, controlling access, correcting drainage problems and implementing excellent hygiene protocols.

Phosphite controls many species of Phytophthora, including Phytophthora cinnamomi. It can be used on native vegetation, horticultural species and ornamental plants. Phosphite is not toxic to people and animals and its toxicity has been compared to table salt. There is a very low pollution risk associated with phosphite. When phosphite is sprayed on to the foliage of plants, it is applied at a very low rate, so any phosphite that reaches the soil is bound to the soil and does not reach the water table.

Phosphite is available from most nurseries, hardware stores and rural supply stores. Treating plants with phosphite is inexpensive - a medium sized jarrah tree requires less than 50 cents worth of chemical to treat.

Phosphite needs to enter a plant's water transport system in order for it to be effective. This can be done by injecting phosphite into trees, or spraying the leaves of understorey plants. In bushland the most common tree species injected include jarrah, snotty gobbles, banksia species, sheoak and woody pears. Only inject trees with a diameter at chest height of 10-14 cm or greater. Phosphite not only protects a plant from Phytophthora dieback infection, it can also help a plant to recover if it is already infected. If a jarrah tree is showing signs of infection, treatment with phosphite can help to save it.

Injecting a tree with phosphite provides three to five years protection from Phytophthora dieback. In contrast, spraying with phosphite provides protection for only one to two years. Because it only provides temporary protection, treatment needs to be ongoing and included in bushland management and future action plans.

Injecting and spraying a large reserve can be a daunting task for a small community group, so consider applying for funding to employ a private contractor such as Dieback Treatment Services (1300 785 311), Conservation Volunteers Australia, Greencorp or similar to assist your group to complete the treatment.

In some cases stressed plants that are treated with phosphite will show signs of leaf burning. In most cases this is a short-term effect and the plant will recover with the change of the seasons. In a small number of cases the plants that are already infected may be killed by the added stress of the phosphite treatment. To reduce the likelihood of any potential leaf burning, the phosphite rates described are chosen from the lower end of the prescribed range. For injecting the rate is five per cent; and for spraying one third of one percent. Prior to undertaking any phosphite treatment of bushland for commercial gain, a contractor must contact the Australian Pesticides and Veterinary Medicine Authority for further information.

1. Injecting Trees

For a step by step guide to injection using the Chemjet® spring loaded syringes please consult the Dieback Working Group fact sheet – injection with syringes.

Equipment

• Phosphite injection can be done with large syringes or with a number of different types of stem injection. equipment, for example the Sidewinder tree injector, Rawlins tree injector or the F1-11 trunk injector.
• Cordless electric drill and an appropriate drill bit (4 mm drill bit with syringes). Follow safety instructions associated with the use of the drill.
• Phosphite - sold in a 20, 40 or 60 per cent solution.
• Personal protective equipment including safety glasses, gloves, well covered shoes and protective clothes.

Timing

The best time to inject a tree is when water is moving within the tree. Water movement is usually greatest in spring and summer. Injecting in the morning is usually more successful than in the afternoon. For further information on storage, disposal of containers and first aid consult the material safety data sheet for your phosphite product.

Preparation to make a 5% solution

• If using 20% phosphite, dilute one part phosphite with 3 parts water.
• If using 40% phosphite, dilute one part phosphite with 7 parts water.
• If using 60% phosphite, dilute one part phosphite with 11 parts water.
• Use a good quality water source, preferably scheme water or rain water.

Procedure

1. Drill a hole into the tree. Injection needs to be in the sapwood, so do not drill any deeper than 2-3 cm. Usually the wood colour will change from the brown bark to white at the correct depth. Drill the hole at waist height so that injecting will be comfortable for you. The hole should be drilled at a slight downward angle.
2. Drill a hole every 20 cm around the tree trunk (approximately one hand span). Multi-stemmed trees need holes in all stems.
3. Follow the instructions that come with the tree injector regarding its set up and use.
4. Insert the nozzle of the syringe or injector into the drilled hole and twist slightly to get a good seal. Slowly push/pump the solution into the tree. Make sure the solution is taken up by the tree and does not run out. Inject 20 mL of the solution into each hole.
5. Monitor plant health. If there is no sign of a decline in plant health, repeat in three to five years' time. If plants show a decline in health prior to three years, repeat treatment.

2. Spraying Plants

The solution for spraying is much weaker than for injecting and contains a small amount of wetting agent or penetrant to hold the droplets on the leaf surface until they are absorbed. Not all understorey plants are at risk but it is easier to spray all plants. Phosphite spraying should not be conducted along creek lines and streams as it can cause adverse effects on some amphibious animals. For a step by step guide to spraying with phosphite please consult the Dieback Working Group fact sheet - spraying.

Equipment

• Backpack sprayer - ensure that it is clean and has not recently contained herbicides or other chemicals.
• Phosphite - sold in a 20, 40 or 60 per cent solution.
• BS1000 (available from Mirco Bros 08 9410 2233) or another wetting agent or penetrant approved for use on native plants. Use rates recommended by the manufacturer.

Timing

Spraying is most effective in spring and summer. Spraying should not occur one day after rain or one day before rain.

Preparation for a 0.3% solution

• For a 20% phosphite solution this is one part phosphite to 40 parts water. Therefore add 150 mL phosphite to 10 L of water.
• For a 40% phosphite solution this is one part phosphite to 80 parts water. Therefore add 75 mL phosphite to 10 L of water.
• For a 60% phosphite solution this is one part phosphite to 120 parts water. Therefore add 50 mL phosphite to 10 L of water.
• Shake well.
• Be sure to add penetrant or wetting agent before use as per the manufacturer's instructions.
• Use the solution immediately and mix frequently.

Procedure for backpack spray unit

1. Place the backpack spray unit on your back and adjust the straps so it is comfortable and the pumping lever is on your preferred side. Adjust the nozzle so it gives a coarse spray to ensure the spray doesn't blow away from the plants.
2. Soak the plants so all leaf surfaces are wet to run off. All understorey plants, including grass trees, should be sprayed. 10 litres of solution should last about 15-20 minutes.
3. Monitor plant health. If there is no sign of a decline in health, repeat in one to two years' time.

Larger spray units, for example a spray trailer, can be used and may be more efficient when treating large areas. The chemical concentration should be the same as the concentrations listed above, and the chemicals should be kept well mixed.

FAQ's on phosphite treatment

1. Where do I start?
2. How often do I need to treat?
3. What plants do I inject and which plants do I spray?
4. What personal protective clothing should I wear?
5. Where can I get equipment & chemicals?
6. How can I get advice or receive training on phosphite treatment?

1. Where do I start?
Identify where the Phytophthora dieback is in the bushland area and as a priority treat the buffer between healthy and diseased vegetation to prevent the movement of the disease into the healthy area. Once complete you can then treat along edges of tracks, paths and within the diseased area. With small infections, such as those in home gardens consider treating all the susceptible species through a complete treatment of spraying and injecting.

2. How often do I need to treat?
You will need to repeat phosphite treatment to maintain the control of the disease. Injecting needs to be conducted very 3-5 years and spraying every 1-2 years.

3. What plants do I inject and which plants do I spray?
In bushland the most common tree species injected include jarrah, snotty gobbles, banksia species, sheoak and woody pears. Only inject trees with a diameter at chest height of 10-14 cm or greater. To complete the treatment spray all other plants including small trees and understorey species such as Grass trees.

In home gardens also consider treating susceptible plants such as roses, fruit trees and azalea's. Also consider replacing dead plants with those resistant to the disease.

4. What personal protective clothing should I wear?
Make sure to always wear old clothing or overalls, gloves, safely glasses and a face mask when spraying. Likewise make sure to wear old clothing or overalls, gloves and safely glasses when injecting. For further information on first aid treatment please consult the material safety data sheet supplied with the chemical.

5. Where can I get equipment & chemicals?
Phosphite treatment gear can be purchased from Dieback Treatment Services (1300 785 311). Alternatively a number of community groups across the south-west hire out the treatment gear, contact the Dieback Working Group (08 9257 9937) for more information. Phosphite, surfactants/penetrants and some limited treatment gear can be purchased from Agricultural supply companies, your local nursery or hardware store.

6. How can I get advice or receive training on phosphite treatment?
You can receive training on Phytophthora dieback management and phosphite treatment by contacting your local community based conservation group, catchment group or the Dieback Working Group.

For further information on the use of Phosphite to control Phytophthora dieback please consult DEC's manual - Phytophthora cinnamomi and disease caused by it. Volume 3 - Phoshite Operations Guidlines.